1. Field of the Invention
The present invention relates to a method of aligning a substrate, a mask to be aligned with the substrate, and a flat panel display apparatus using the same. More particularly, the present invention relates to a method of providing efficient alignment of an opaque substrate with a patterning/deposition mask.
2. Description of the Related Art
Generally, flat panel display apparatuses have thin and light display panels exhibiting superior display characteristics as compared to other display devices, e.g., excellent visibility, wide viewing angles, high contrast, and high response speed. For example, an organic electroluminescent (EL) display device, i.e., a display device employing voltage between two electrodes to excite electrons in an organic light emitting layer between the electrodes, may further exhibit high luminance and driving voltage to enable improved color purity and display.
Manufacturing of flat panel apparatuses may require, inter alia, deposition and patterning of thin films. Conventional methods of thin film deposition on a substrate may include a vacuum evaporation method, an ion plating method, a sputtering method, a chemical vapor deposition method, and so forth. Conventional methods of patterning may include wet etching. For example, manufacturing of the conventional organic EL display device may require deposition of at least one electrode, i.e., a first electrode, and an organic light emitting layer by the vacuum evaporation method, followed by patterning via wet etching, e.g., photolithography. In order to minimize deterioration of the organic light emitting layer during the wet etching, e.g., due to contact with moisture and oxygen, simultaneous film deposition and patterning may be performed. For example, the conventional method of simultaneous film deposition and patterning may provide attachment of a mask with a predetermined pattern to a substrate, so that material deposited onto the substrate via the mask may be formed at the predetermined pattern of the mask.
However, simultaneous deposition and patterning may require accurate alignment between the substrate and the mask. For example, a conventional alignment of a mask and a flexible substrate, e.g., a synthetic resin, may require a complex procedure for aligning multiple layers, e.g., a light emitting layer, a driving thin film transistor layer, an electrode layer, and so forth, while imparting minimized deformation to the flexible substrate. On the other hand, a conventional alignment of a mask and an opaque substrate, e.g., a metal substrate, may require accurate alignment via alignment holes in the opaque substrate and the mask.
However, due to the opaque material employed to form the opaque substrate, the reflectance thereof may be similar to the reflectance of the mask, thereby reducing visibility of a boundary line between the substrate and the mask. As such, accurate alignment of the substrate and the mask may be difficult, while a confirmation of a proper alignment via optical devices, e.g., an optical sensor, may be incorrect. Accordingly, there exists a need for a method capable of providing effective alignment of an opaque substrate with a mask.